Protective device for refrigeration compressors

ABSTRACT

A protective device for protection of a refrigeration compressor from burnout caused by short cycling. A time delay means is provided which prevents the compressor motor from being started again until a predetermined time interval has elapsed after the system thermostat has opened. If a power failure should occur, the compressor motor is prevented from being started until a predetermined time interval has elapsed after power resumption to the refrigeration system.

United States Patent [191 Weihl [451 Mar. 12, 1974 PROTECTIVE DEVICE FORREFRIGERATION COMPRESSORS [75] Inventor: Steven P. Weihl, Logansport,Ind.

[73] Assignee: Essex International, Inc., Ft. Wayne,

Ind.

[22] Filed: Dec. 15, 1972 [21] Appl. No.: 315,341

[52] US. Cl 62/158, 307/293, 318/484 [51] Int. Cl. G05d 23/32 [58] Fieldof Search 62/158; 318/484; 307/293 [5 6] References Cited UNITED STATESPATENTS 3,127,754 4/1964 Mobarry 62/158 3,707,661 12/1972 King 62/158Primary Examiner-Meyer Perlin Attorney, Agent, or Firm-Robert D. Sommer[5 7 ABSTRACT A protective device for protection of a refrigerationcompressor from burnout caused by short cycling. A time delay means isprovided which prevents the compressor motor from being started againuntil a predetermined time interval has elapsed after the systemthermostat has opened. If a power failure should occur, the compressormotor is prevented from being started until a predetermined timeinterval has elapsed after power resumption to the refrigeration system.

6 Claims, 1 Drawing Figure PATENTEUMAR 12 um M OTOR PROTECTIVE DEVICEFOR REFRIGERATION COMPRESSORS BACKGROUND OF THE INVENTION The presentinvention is concerned with refrigeration systems and, in particular, isconcerned with preventing burnout of the compressor motor caused byshort cycling.

in the past, refrigeration systems have been protected from compressorshort cycling. However, these previous protective devices do not alwaysafford complete protection.

In one prior art system a timing motor in conjunction with a cam is usedto prevent compressor short cycling. When the system thermostat opens,the timing motor is actuated and prevents the compressor from beingstarted until the timing motor has timed the proper interval. However,if a power failure should occur while the system thermostat is closed,it is possible that the compressor motor will be restarted when power isresumed to the system. And if the power failure is short enough induration, the compressor can short cycle, possibly burning out thecompressor motor.

Another prior art device employs a bimetallic element as a time delaymeans. When the system thermostat opens the bimetallic element preventsreenergization of the contactor controlling the compressor motor untilthe time interval has elapsed. If a power failure should occur while thethermostat is closed, compressor short cycling is still possible.

SUMMARY OF THE INVENTION This protective device recognizes the openingof the system thermostat or other limit device. Then in response to thisopening a time delay means is energized. The purpose of the time delaymeans is to prevent the contactor which controls the compressor motorfrom being energized until a predetermined time interval has elapsedafter the thermostat or other limit device has opened. A first relay anda time delay circuit are both energized when the system thermostat orlimit device opens. After a predetermined time interval has elapsed, thetime delay. circuit acts to deenergize the first relay allowing thecontactor to be energized upon thermostat closure. The contactor can beenergized only when the system thermostat and all limit devices areclosed and the first relay is deenergized. A second latching relay isprovided to prevent compressor short cycling when a power failure hasoccurred.

Further features and advantages of the invention will be apparent fromthe following description and accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single drawing FIGURE illustratesschematically a wiring diagram of a refrigeration system including apresently preferred form of a compressor motor protective device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, thereis shown an electric motor I for driving the refrigerant compressor of aconventional compressor-condensor-evaporator type refrigeration system.The motor 1 is connected to alternating current electric supply lines 2,3 and 4 through contactor switches 5a, 5b and 5c. The contactor switchesare closed by a contactor coil 5 connected in a control circuit whichmay have its terminals connected to the supply lines 3 and 4. Thecontrol circuit further includes a thermostat 6 or another suitablecondition responsive switch responsive to refrigeration system demandand may also include one or more safety or limit switches 7 such as alow-pressure switch, a high-pressure switch and a motor thermal overloadswitch.

Time delay means 8 is provided to prevent energization of contactor coil5 until it has been deenergized for a predetermined time interval. Diode9 provides suitable rectification..Resistors l0 and 13 and capacitors 12and 14 provide filtering for the time delay circuit 16 which isdescribed later. An impedance relay coil 15 .has corresponding normallyclosed contacts 15a and normally open contacts 15b in series withcontactor coil 5, thermostat 6 and safety or limit switches 7. Alatching relay with coil 17 and normally open contact 17a protects therefrigeration system in case of a power failure.

Time delay circuit 16 employs a programmable unijunction transistor(PUT) indicated generally by reference character 18 having anodeelectrode 18a, cathode electrode 18k, and gate electrode 18g. Resistor19, capacitor 20, resistor 21 and resistor 22 act in conjunction to firethe PUT 18 after the proper time interval has elapsed. Resistor 25limits the current through the anode cathode circuit of SCR 26, andresistor 23 and I 24 bias the gate electrode of SCR 26 properly.

The time delay circuit 16 operates in the following manner:

When power is applied to the system or when thermostat 6 or limit'switchof switches 7 open, the time delay circuit is actuated. Capacitor 20begins to charge and when the voltage at the gate electrode 18g of PUT18 becomes slightly negative with respect to the voltage at 18a, PUT l8fires closing a conduction path between the anode 18a and the cathode18k. This applies a voltage to the gate of SCR 26, allowing the SCR 26to conduct and latch.

The operation of the protective device for refrigeration compressors isas follows:

Upon application of power to the system through power lines 3 and 4,relay coil 15 and time delay circuit 16 will both be energized. Sincetime delay means 8 does not draw enough current, contactor coil 5 willremain deenergized. When relay coil 15 is energized contacts 15a and 15bwill transfer. This allows relay coil 17 to be energized, closingcontacts 17a. After the predetermined time interval has been timed bythe timing circuit 16 as previously described, SCR 26 will latch,deenergizing relay coil 15 and restoring contacts 15a and 15b to theirnormal positions. Assuming thermostat 6 and limit switch 7 are closed, acurrent path will be created through contactor coil 5, thermostat 6,limit switch 7, normally closed contacts 15a and closed contacts 17a.Contactor coil 5 is energized through this path. If the thermostatshould be open when relay coil 15 is deenergized by SCR 26, the circuitwill remain in this condition and contactor coil 5 will be energizedwhen thermostat 6 closes.

It can be seen that contactor coil 5 cannot be energized after thethermostat 6 opens until the time delay circuit 16 has timed the properinterval and deenergized relay coil 15.

If a power failure should occur, contactor coil 5 cannot be reenergizeduntil relay coil 15 has been energized, relay coil 17 has been energizedand relay coil 15 has been deenergized by SCR 26.

As a specific example, the following circuit components operated aspreviously described although certain changes can be made withoutdeparting from spirit of the invention:

Diode 9 lN 4002 Resistor 10 22 ohm Capacitor 12 3.3 mfd.

Resistor 13 I000 ohm Capacitor 14 3.3 Mfd Relay Coil 15 Essex ControlsDivision Type M564 Relay Coil 17 Essex Controls Division Type 184 PUT 182N6027 Resistor 19 14.7 Megohm Capacitor 20 20 Mfd.

Resistor 21 2.2. Megohm Resistor 22 3.9 Megohm Resistor 23 22 ohmResistor 24 1000 ohm Resistor 25 22 ohm SCR 26 General Electric C 106 FWhat is claimed is:

1. A protective device for use with a refrigeration system having arefrigerant compressor driven by an electric motor, a contactorswitching device including a contactor coil and a contactor switch forclosing an energizing circuit to saidmotor when said contactor coil isenergized, a condition responsive switch means responsive torefrigeration system demand, and a control circuit for energizing saidcontactor coil having two terminals for connection to a source ofelectric power, said control circuit including said contactor coil andsaid condition responsive switch means in series with said contactorcoil being connected to one of said terminals, said protective devicecomprising:

an impedance relay having an impedance coil and a normally closed switchwhich opens when said impedance relay coil is energized;

means for connecting said normally closed impedance relay switch in saidcontrol circuit between said condition responsive switch means and theother of said terminals to prevent energization of said contactor coilwhen said normally closed impedance relay switch is open;

means for connecting said impedance relay coil across said otherterminal and the junction of said contactor coil with said conditionresponsive switch means for energization of said impedance relay hailfrom said source of electric power through said contactor coil;

' and time delay means connected in parallel with said impedance relaycoil for deenergizing'said impedance relay coil a predetermined intervalof time after said time delay means is energized.

2; A protective device according to claim 1- wherein said time delaymeans comprises:

semiconducted switching means connected said impedance relay coil andoperative to substantially 1 short out said impedance relay coil whensaid semiconductor switching means is in a conductive state;

and a time delay circuit connected to said semiconductor switching meansand operative to render said semiconductor switching means conductive apredetermined interval of time after said time delay meansis energized.

3. A protective device according to claim 2 wherein:

a diode member connects said impedance relay coil and said time delaymeans to the junction of said contactor coil with said conditionresponsive switch means;

said semiconductor switching means is a silicon controlled rectifierhaving anode andcathode electrodes connected across said impedance relaycoil;

and said time delay circuit comprises a resistancecapacitance timingcircuit and a programmable unijunction transistor responsive toenergization of said resistance-capacitance timing circuit for apredetermined interval of time to provide a firing signal to the gateelectrode of said silicon controlled rectifier.

4. A protective device according to claim 1 further comprising:

alatching relay having a coil and a normally open switch which closeswhen said latching relay coil is energized;

a normally open impedance relay switch which closes when said impedancerelay coil is energized;

means for connecting said latching relay switch and said normally openimpedance relay switch in parallel with each other in said controlcircuit between said normallyclosed impedance relay switch and saidother terminal;

and means for connecting said latching relay coil between said oneterminal and the junction of said normally closed impedance relay switchwith said latching relay switch and said normally open impedance relayswitch. I

5. A protective device according to claim 4 wherei said time delay meanscomprises:

semiconductor switching means connected to said impedance relay coil andoperative to substantially short out said impedance relay coil when saidsemiconductor switching means is in a conductive state;

and a time delay circuit connected to said semiconductor switching meansand operative to render said semiconductor switching means conductive apredetermined interval of time after said time delay means is energized.

6. A protective device according to. claim 5 wherein:

a diode member connects said impedance relay coil and said time delaymeans to the junction of said contactor coil with said conditionresponsive switch means;

said semiconductor switching means is a silicon controlled rectifierhaving anode and cathode electrodes connected across said impedancerelay coil;

rectifier. v

1. A protective device for use with a refrigeration system having arefrigerant compressor driven by an electric motor, a contactorswitching device including a contactor coil and a contactor switch forclosing an energizing circuit to said motor when said contactor coil isenergized, a condition responsive switch means responsive torefrigeration system demand, and a control circuit for energizing saidcontactor coil having two terminals for connection to a source ofelectric power, said control circuit including said contactor coil andsaid condition responsive switch means in series with said contactorcoil being connected to one of said terminals, said protective devicecomprising: an impedance relay having an impedance coil and a normallyclosed switch which opens when said impedance relay coil is energized;means for connecting said normally closed impedance relay switch in saidcontrol circuit between said condition responsive switch means and theother of said terminals to prevent energization of said contactor coilwhen said normally closed impedance relay switch is open; means forconnecting said impedance relay coil across said other terminal and thejunction of said contactor coil with said condition responsive switchmeans for energization of said impedance relay coil from said source ofelectric power through said contactor coil; and time delay meansconnected in parallel with said impedance relay coil for deenergizingsaid impedance relay coil a predetermined interval of time after saidtime delay means is energized.
 2. A protective device according to claim1 wherein said time delay means comprises: semiconducted switching meansconnected said impedance relay coil and operative to substantially shortout said impedance relay coil when said semiconductor switching means isin a conductive state; and a time delay circuit connected to saidsemiconductor switching means and operative to render said semiconductorswitching means conductive a predetermined interval of time after saidtime delay means is energized.
 3. A protective device according to claim2 wherein: a diode member connects said impedance relay coil and saidtime delay means to the junction of said contactor coil with saidcondition responsive switch means; said semiconductor switching means isa silicon controlled rectifier having anode and cathode electrodesconnected across said impedance relay coil; and said time delay circuitcomprises a resistance-capacitance timing circuit and a programmableunijunction transistor responsive to energization of saidresistance-capacitance timing circuit for a predetermined interval oftime to provide a firing signal to the gate electrode of said siliconcontrolled rectifier.
 4. A protective device according to claim 1further comprising: a latching relay having a coil and a normally openswitch which closes when said latching relay coil is energized; anormally open impedance relay switch which closes when said impedancerelay coil is energized; means for connecting said latching relay switchand said normally open impedance relay switch in parallel with eachother in said control circuit between said normally closed impedancerelay switch and said other terminal; and means for connecting saidlatching relay coil between said one terminal and the junction of saidnormally closed impedance relay switch with said latching relay switchand said normally open impedance relay switch.
 5. A protective deviceaccording to claim 4 wherein said time delay means comprises:semiconductor switching means connected to said impeDance relay coil andoperative to substantially short out said impedance relay coil when saidsemiconductor switching means is in a conductive state; and a time delaycircuit connected to said semiconductor switching means and operative torender said semiconductor switching means conductive a predeterminedinterval of time after said time delay means is energized.
 6. Aprotective device according to claim 5 wherein: a diode member connectssaid impedance relay coil and said time delay means to the junction ofsaid contactor coil with said condition responsive switch means; saidsemiconductor switching means is a silicon controlled rectifier havinganode and cathode electrodes connected across said impedance relay coil;and said time delay circuit comprises a resistance-capacitance timingcircuit and a programmable unijunction transistor responsive toenergization of said resistance-capacitance timing circuit for apredetermined interval of time to provide a firing signal to the gateelectrode of said silicon controlled rectifier.